The present invention relates to method and apparatus for sensing passage of a moving element, and more particularly to method and apparatus for detecting revolutions of a dial arm of a utility meter.
Metering devices are used by utility companies to register the amount of gas, electricity, water, etc. consumed by residential users. These utility meters generally are mechanical devices having a meter face including a number of dials which register utility usage in increments of tens of units, hundreds of units, thousands of units, etc. Such utility meters, most notably gas meters but also water and electric meters, are generally located inside the private homes of the residential customers and are therefore not readily accessible to utility company employees. The meter readings must be periodically taken, however, in order to check the amount of utility usage and determine the appropriate bill to be forwarded to the customer. This is troublesome for both the customer and the utility company.
It has long been recognized that it would be preferable if the readout of the utility meter were mounted outside of the customer's home. The utility meter reader would then have unimpeded access to the meter, and the number of occasions upon which the customer would have to be disturbed by the utility company would be substantially reduced. Unfortunately, it would be prohibitively expensive for a utility company to replace existing, internal utility meters with other meters capable of being read from outside the customer's residence.
One other method of accomplishing the same goal would be to modify existing utility meters in such a manner that utility usage could be read from outside of the customer's residence. Such a retrofit system is described in the corresponding U.S. patent application of Sears, Ser. No. 311,531, filed Oct. 15, 1981. In the system described in that patent application, a small trip device is mounted on the face of the existing utility meter. The trip device is tripped by one of the dial arms of the meter face, once each revolution, and provides one electrical pulse each time it is thus tripped. The electrical pulses are applied to a counting circuit which thus accumulates a count representative of utility usage. The counter can easily be coupled to an external readout so that the accumulated count can be read from outside of the customer's home.